Touch screens have become a preferred user input device for smartphones and tablet computers. Touch screens use a transparent touch sensor panel overlying a display screen, e.g., a Liquid Crystal Display (LCD). Touch screens provide a more intuitive and natural way to interact with a Graphical User Interface (GUI) compared to traditional pointing devices such as mice or touch pads.
One form of touch screen has an array of diamond-shaped transparent, electrically-conductive areas formed on a transparent panel. (An alternative design uses square-shaped areas.) Half of the diamond shaped areas may be connected in horizontal rows and half connected together to form vertical columns. Electrical waveforms may be applied to the rows and sensed on the columns, or vice versa. The rows and columns may be scanned in a raster pattern in order to interrogate each X-Y position on the screen. If a user positions a finger tip at a certain position on the screen, the user's finger tip will alter the capacitive coupling between the row and column that cross at the position and when the aforementioned raster scanning addresses this position, the alteration of the capacitive coupling will be sensed by a change in the signal coupling from the row to the column or vice versa.
The diamond shaped areas are connected together by relatively narrow (compared to diamond width) traces so as to form rows and columns. The traces of the rows and the columns must not touch so as to avoid electrical short circuits. The traces of either the rows or the columns can be disposed in a common plane with the diamond shaped areas and formed in the same process used to form the diamond shaped areas; however, other traces which cross over those disposed in the common plane are formed in subsequent processes, i.e., by depositing an insulating material over the in-plane traces and subsequently forming conductive bridging traces from sputtered metal. The additional processes of depositing the insulating material and forming the bridging traces introduce new opportunities for defects to occur. Defects can also occur in the in-plane traces, which may result in portions of a row or column being electrically disconnected. Such defects tend to lower the yield of the touch sensor panel manufacturing process leading to decreased productivity and increased panel cost.
Accordingly it would be desirable to provide a touch sensor panel that is less prone to failure due to one or more connection failures.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the various embodiments.